EP1988676A1 - Détermination d'une erreur de fréquence dans un récepteur d'un système de communication sans fil - Google Patents

Détermination d'une erreur de fréquence dans un récepteur d'un système de communication sans fil Download PDF

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Publication number
EP1988676A1
EP1988676A1 EP07388030A EP07388030A EP1988676A1 EP 1988676 A1 EP1988676 A1 EP 1988676A1 EP 07388030 A EP07388030 A EP 07388030A EP 07388030 A EP07388030 A EP 07388030A EP 1988676 A1 EP1988676 A1 EP 1988676A1
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Prior art keywords
phase difference
change
pilot cells
sub
pilot
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EP07388030A
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German (de)
English (en)
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EP1988676B1 (fr
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Bengt Lindoff
Fredrik Nordström
Leif Wilhelmsson
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Telefonaktiebolaget LM Ericsson AB
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Telefonaktiebolaget LM Ericsson AB
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Priority to EP07388030.4A priority Critical patent/EP1988676B1/fr
Priority to PCT/EP2008/055454 priority patent/WO2008135541A1/fr
Priority to US12/598,613 priority patent/US8270509B2/en
Priority to JP2010504752A priority patent/JP5309132B2/ja
Publication of EP1988676A1 publication Critical patent/EP1988676A1/fr
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2657—Carrier synchronisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2602—Signal structure
    • H04L27/261—Details of reference signals
    • H04L27/2613—Structure of the reference signals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2668—Details of algorithms
    • H04L27/2673—Details of algorithms characterised by synchronisation parameters
    • H04L27/2675—Pilot or known symbols

Definitions

  • the invention relates to determining, in a receiver of a wireless communications system employing Orthogonal Frequency Division Multiplexing, a frequency error of received signals compared to corresponding signals generated in the receiver.
  • VoIP Voice over Internet Protocol
  • the data is transmitted in something referred to as a resource block, which corresponds to data being sent using a certain number of sub-carriers during a certain time, e.g. corresponding to a few symbols.
  • a resource block can be sent at regular intervals. For instance, if the duration of a resource block is 0.5 ms, a resource block transmitted every 20 ms might suffice in order to support VoIP. In fact, it might be that single resource blocks are transmitted at even longer intervals, implying that it might not be feasible to estimate time and frequency using two or more resource blocks.
  • Frequency estimation algorithms are well known in the art and used both in GSM and WCDMA and are also used in current OFDM systems like Digital Video Broadcast - Handheld (DVB-H) and Wireless Local Area Network (WLAN).
  • the OFDM signal comprises many separately-modulated sub-carriers, each symbol may be considered to be divided into cells, each corresponding to the modulation carried on one sub-carrier during one symbol.
  • Some of these cells are pilot cells that are modulated with reference information, whose transmitted value is known to the receiver.
  • the cells may also be referred to as resource elements, and pilot cells may be referred to as pilot symbols or reference symbols. In the following the terms cells and pilot cells will be used.
  • phase difference between two pilot cells that are on two adjacent sub-carriers and in consecutive OFDM symbols, and finds a certain phase difference, it might be because of the channel, it might be because of sub-carrier frequency offset, or it might be because of a combination of both. In any event, it is obviously so that the accuracy of the frequency estimate based on the above mentioned phase difference will be limited by the uncertainty regarding how frequency selective the channel is.
  • frequency estimation if done after the FFT according to the prior art, relies on pilot cells being transmitted on the same sub-carrier. When this is the case the frequency can be estimated using well-known methods. If the transmission is continuous, or at least the data is sent in long enough packets, this requirement is typically fulfilled. However, if data is transmitted in very short bursts, like single resource blocks, then there will typically not be more than one pilot available on a single sub-carrier, making standard approaches for frequency estimation useless.
  • the object is achieved in a method of determining, in a receiver of a wireless communications system employing Orthogonal Frequency Division Multiplexing, a frequency error of received signals compared to corresponding signals generated in the receiver; wherein the received signals comprise symbols, each symbol of a given duration being transmitted as a number of cells on a corresponding number of sub-carrier frequencies; and wherein some of said cells are pilot cells modulated with reference information whose transmitted value is known to the receiver; the method comprising the step of determining a change from one symbol to another of a phase difference between said received and generated signals.
  • the method further comprises the steps of selecting at least three pilot cells from at least two different symbols, each of said at least three pilot cells being selected from a different sub-carrier frequency; determining a position for each of said at least three pilot cells, the position of a pilot cell being defined as the symbol and the sub-carrier frequency on which the pilot cell is transmitted; determining for each of said at least three pilot cells a phase difference between said received and generated signals; calculating from said determined phase differences and the positions of each of said at least three pilot cells a change in phase difference caused by said frequency error; and calculating the frequency error from said calculated change in phase difference.
  • the phase difference between the received signals and the signals generated in the receiver for a pilot cell may change as a function of the frequency error, which depends on the time, and as a function of the sub-carrier of the cell.
  • the change with time i.e. due to the frequency error, can normally be considered as being linear, at least within a few symbols as it is the case for a single resource block.
  • the difference between the sub-carrier frequencies of the pilot cells is not too big, as it would be the case within a resource block, and/or if the frequency selective channel is approximately linear, it will also be possible to approximate the sub-carrier dependent phase change as a linear change.
  • the phase difference varies in a linear plane as a time and sub-carrier frequency.
  • the step of calculating the change in phase difference caused by said frequency error may further comprise the steps of determining for each of at least two selected pairs of said at least three pilot cells a weighting factor in dependence of a distance in sub-carrier frequency and a distance in time between the two cells of the pair; determining for each selected pair a change of phase difference between the two pilot cells of the pair; and calculating said change in phase difference caused by said frequency error as a weighted sum of said determined phase changes by using said determined weighting factors.
  • Using such weighting factors ensures that the weighted sum provides the change in phase difference caused by the frequency error, or in other words that the effect of the sub-carrier dependent phase change is cancelled. It is noted that dependent on how the pairs of pilot cells are selected the weighting factors may be positive or negative.
  • the method further comprises the step of selecting the pairs of pilot cells such that the two pilot cells of each pair are received in different symbols.
  • the method may further comprise the step of performing the calculating steps using phase representation.
  • the method further comprises the step of selecting the pilot cells from only two different symbols; and calculating said change in phase difference caused by said frequency error as a weighted average of said determined phase changes, a relatively simple method of calculating the change in phase difference caused by the frequency error is achieved.
  • the method further comprises the step of selecting the pilot cells such that the sum of the sub-carrier frequencies for the pilot cells selected from one of the two different symbols substantially equals the sum of the sub-carrier frequencies for the pilot cells selected from the other one of the two different symbols; and calculating said change in phase difference caused by said frequency error as the average of said determined total phase changes, the computational complexity is kept at a minimum.
  • the method may further comprise the step of performing the calculating steps using complex representation.
  • the method further comprises the step of selecting the pairs of pilot cells such that at least the two pilot cells of a first pair are received in the same symbol.
  • the step of calculating the change in phase difference caused by said frequency error may further comprise the steps of determining the change of phase difference between the two pilot cells of said first pair; calculating therefrom a sub-carrier frequency dependent change of phase difference; determining the change of phase difference between the two pilot cells of a second pair that is received in different symbols; and calculating said change in phase difference caused by said frequency error by subtracting the calculated sub-carrier frequency dependent change of phase difference multiplied by a factor indicating the distance in sub-carrier frequency between the pilot cells of said second pair from the change in phase difference determined for the second pair.
  • This means that effectively the sub-carrier dependent phase change is estimated first, and its effect is then subtracted from the total phase change measured between a pair of pilot cells chosen from different symbols and different sub-carriers.
  • the step of calculating the change in phase difference caused by said frequency error is performed by least squares estimation. This embodiment is especially feasible when more than three pilot cells are available for the estimation.
  • the invention also relates to a receiver for a wireless communications system employing Orthogonal Frequency Division Multiplexing, wherein the received signals comprise symbols, each symbol of a given duration being transmitted as a number of cells on a corresponding number of sub-carrier frequencies; and wherein some of said cells are pilot cells modulated with reference information whose transmitted value is known to the receiver; the receiver being arranged to determine a frequency error of received signals compared to corresponding signals generated in the receiver by determining a change from one symbol to another of a phase difference between said received and generated signals.
  • Orthogonal Frequency Division Multiplexing wherein the received signals comprise symbols, each symbol of a given duration being transmitted as a number of cells on a corresponding number of sub-carrier frequencies; and wherein some of said cells are pilot cells modulated with reference information whose transmitted value is known to the receiver; the receiver being arranged to determine a frequency error of received signals compared to corresponding signals generated in the receiver by determining a change from one symbol to another of a phase difference between said received and generated
  • the receiver comprises means for selecting at least three pilot cells from at least two different symbols, each of said at least three pilot cells being selected from a different sub-carrier frequency, and determining a position for each of said at least three pilot cells, the position of a pilot cell being defined as the symbol and the sub-carrier frequency on which the pilot cell is transmitted, means for determining for each of said at least three pilot cells a phase difference between said received and generated signals, means for calculating from said determined phase differences and the positions of each of said at least three pilot cells a change in phase difference caused by said frequency error, and means for calculating the frequency error from said calculated change in phase difference, then a receiver capable of determining a frequency error also in situations where only a short data burst, such as a single resource block, is available for the estimation is provided.
  • Embodiments corresponding to those mentioned above for the method also apply for the receiver.
  • the receiver may be a receiver of a mobile telephone.
  • the invention also relates to a computer program and a computer readable medium with program code means for performing the method described above.
  • Orthogonal Frequency Division Multiplexing a multi carrier approach, in which an original data stream is multiplexed into a number of parallel data streams with a correspondingly low symbol rate, is used to reduce inter symbol interference (ISI) by reducing the symbol rate without reducing the data rate.
  • ISI inter symbol interference
  • the inter symbol interference is caused by delay spread of the channel impulse response for the multipath channel over which the signals are transmitted.
  • Each of the parallel data streams are modulated with a different sub-carrier frequency and the resulting signals are transmitted together in the same band from a transmitter to a receiver.
  • a high number of different sub-carrier frequencies i.e. several hundreds or even thousands, will be used, and these frequencies need to be very close to each other.
  • FFT Fast Fourier Transform
  • each OFDM symbol constituted by the set of sub-carriers is transmitted with a duration T S , which is composed of two parts, a useful part with duration T U and a guard interval (GI) or cyclic prefix (CP) with a duration T G .
  • the guard interval consists of a cyclic continuation of the useful part T U and precedes the symbol as a prefix. This is illustrated in Figure 1 , in which T U is the length of the useful part of the symbol, while T G is the length of the guard interval. As long as T G is longer than the maximum channel delay, all reflections of previous symbols can be removed in the receiver by disregarding the guard interval, and inter symbol interference can thus be avoided.
  • each symbol is considered to be divided into cells, each corresponding to the modulation carried on one sub-carrier during one symbol.
  • Frequency estimation algorithms are well known in the art and used e.g. in GSM and WCDMA systems, and they are also used in current OFDM systems like DVB-H and WLAN. The basic idea with these algorithms is to consider how much the phase has changed between two instants of time.
  • Pilot cells are cells within the OFDM frame structure that are modulated with reference information, whose transmitted value is known to the receiver.
  • the information may be transmitted as continual pilot cells or scattered pilot cells. This is illustrated in Figure 2 showing a number of transmitted symbols ( n , n +1, n +2, ...), each comprising a number of cells ( l -6 to l +6) corresponding to the sub-carriers.
  • White cells are data cells, while the black cells are pilot cells.
  • Continual pilot cells are shown in sub-carrier l -6, where the pilot information is sent continuously, i.e.
  • the scattered pilot cells are transmitted on some sub-carriers intermittently.
  • Continual pilot cells on a given sub-carrier can easily be used for detecting a change of phase between two instants of time, since the pilot information is sent continuously on that sub-carrier.
  • the change of phase between two instants of time can be detected by comparing two pilot cells from the same sub-carrier. As an example, for sub-carrier l -3 the pilot cells from symbols n +1 and n +5 can be compared.
  • a single resource block can be sent at regular intervals. For instance, if the duration of a resource block is 0.5 ms, a resource block transmitted every 10 ms might suffice to support VoIP. In fact, it might be that single resource blocks are transmitted at even longer intervals.
  • phase difference between two symbols that normally would be used as an adequate measure of the frequency offset essentially becomes useless for frequency offset estimation.
  • pilot cells transmitted on different sub-carriers are not well suited for frequency offset estimation because the phases for the different sub-carriers are typically affected in a different and unknown way.
  • Reasons why different sub-carriers are affected differently might be that the channel as such is frequency selective, but it might also be caused by a synchronization error.
  • the channel is frequency selective is considered, and it is supposed that the channel consists of two taps of equal strength and with a delay between the two that equals ⁇ t seconds.
  • phase difference between two pilot symbols that are on two adjacent sub-carriers and in consecutive OFDM symbols, and finds that the phase difference equals 0.094, it might be because of the channel, it might be because of frequency offset, or it might be because a combination of both. In any event, it is obviously so that the accuracy of the frequency estimate based on such phase difference will be limited by the uncertainty regarding how frequency selective the channel is.
  • the FFT window is placed ⁇ samples earlier than the latest possible position in order to avoid ISI, as seen in Figure 4 . It is noted that in this case the start of the FFT window (the samples used by the FFT) is placed in the middle of the ISI free part of the guard interval.
  • frequency estimation in particular if done after the FFT, relies on the fact that pilot symbols are transmitted on the same sub-carrier. When this is the case, the frequency can be estimated using well-known methods. If the transmission is continuous, or at least the data is sent in long enough packets, this requirement is typically fulfilled. However, if data is transmitted in very short bursts, like single resource blocks, then there will typically not be more than one pilot available on a single sub-carrier, making standard approaches for frequency estimation useless.
  • the described algorithms use pilot symbols in such a way that the effect of the sub-carrier frequency dependent phase rotation is cancelled, thus allowing the frequency error to be estimated, or they actually estimate the frequency dependent phase rotations. This might for instance be done jointly with estimating the frequency error, or it might be done separately.
  • the problem with a frequency dependent phase rotation is circumvented by choosing the pilot cells used for frequency estimation in such a way that the frequency dependent phase rotation is cancelled, or at least is small enough for the frequency error to be estimated with sufficient accuracy. This is achieved by properly choosing what pilots to be used for frequency estimation, and the solution is based on the assumption that when the sub-carriers of the chosen pilot cells are relatively close to each other, the frequency dependent phase rotation can be considered as a linear function.
  • p n,l denotes the pilot that is transmitted on sub-carrier l in OFDM symbol n
  • the frequency offset is to be estimated using pilots from symbol n and n + 1
  • two pairs of pilots in these two OFDM symbols can be used such that the sum of the indexes of the sub-carriers used for each of the two OFDM symbols is as similar as possible, and preferably equal.
  • Figure 5 shows how the pilot symbols might be interlaced with the data symbols in time and frequency for a resource block consisting of only two symbols, and how two pairs of pilots may be selected.
  • pilot cells p n , l and p n+1 , l+3 are used. This will result in a phase shift that is due to frequency error plus the frequency dependent phase shift that is due to the pilots being three sub-carriers apart.
  • symbols p n , l and p n+1 , l-3 are used. Again this will result in a phase shift that is due to frequency error plus the frequency dependent phase shift that is due to the pilots being three sub-carriers apart.
  • pilot cells p n,l-6 and p n+1,l-3 as the first pair
  • pilot cells p n,l+6 and p n+1,l+3 as the second pair, provided that the channel is not different for the two pairs, because in that case the imaginary part would not be cancelled out.
  • the computational complexity is kept at a minimum.
  • pilots are necessarily used, and some might be used more than once in order to fulfil the requirement of being insensitive to frequency dependent phase shifts, implying that the resulting estimate should be able to improve.
  • the pilot positions might not be suitable for this embodiment.
  • This embodiment might either be carried out in the phase domain, or it might be carried out using complex representation of the signal.
  • pilot cells can not be selected so that the sum of the indices for the sub-carriers is the same for each symbol, estimating the frequency offset can instead be based on a weighted average of the measured phase differences.
  • FIG 6 the pilot cell p n+1,l-3 is used twice while each of p n,l+3 and p n,l-6 is used once.
  • pilot cells p n+1,l-3 and p n,l+3 are used. This will result in a phase shift that is due to frequency error plus the frequency dependent phase shift that is due to the pilots being six sub-carriers apart.
  • symbols p n+1,l-3 and p n , l-6 are used.
  • the frequency error can be estimated from the measured phase rotations without estimating the "unknown" frequency dependent phase rotation. If this is done in the phase domain, and the phase is assumed to vary in a linear fashion, then this allows for the frequency error to be estimated if tree pilot cells are available.
  • Figure 7 illustrates how this can be done by means of three pilot cells p 0 . p 1 and p 2 .
  • the variables used in the figure and the below equations have the following meaning:
  • phase rotation ⁇ x relating to the frequency error can be calculated as a weighted sum of the phase rotations ⁇ 1 and ⁇ 2 measured for the two set of pilot cells shown in Figure 7 .
  • the weighting factors c 2 c 1 + c 2 and c 1 ⁇ d c 1 + c 2 are calculated from the distances in time and sub-carrier frequency between the used pilot cells.
  • ⁇ x is calculated as a weighted average of the measured phase rotations ⁇ 1 and ⁇ 2 .
  • the frequency error can be estimated from the phase differences measured between a number of pilot cells in such a way that the sub-carrier frequency dependent phase rotation does not affect the result.
  • the estimation of the frequency error was done in the phase domain.
  • the estimation of frequency error may also be done using complex representation of the signal, rather than the phase. This is described in the following.
  • a pilot cell constellation corresponding to Figure 5 i.e. a situation in which the (time, sub-carrier)-positions ( n, l - ⁇ ) and ( n, l + ⁇ ), which can be correlated with the pilot in ( n + k, l ), can not be found.
  • this can be the case when the pilot in position ( n, l ) in Figure 5 does not exist.
  • no pair for addition and correlation can be found that fulfils the symmetry conditions described in relation to Figure 5 .
  • pilot p n,l -6 correlated with p n+1,l -3
  • Two weights w 1 and w 2 may be introduced in equation (11), which utilize that the two received pilots at time n are not at the same absolute distance in frequency from the received pilot at time n + k, w 1 ⁇ X n , l - c 1 ⁇ ⁇ p n , l - c 1 ⁇ ⁇ + w 2 ⁇ X n , l - c 2 ⁇ ⁇ p n , l - c 2 ⁇ ⁇ ⁇ X n + k , l * p n + k , l * .
  • a first order Taylor expansion around X n+k,l is performed on the received pilots at time n .
  • the disturbance and higher order terms are assumed to be negligible. This is compared with the preferable value e i (- k ⁇ t ) .
  • the weights are reasonable since if e.g. c 1 ⁇ c 2 , the first pilot is closer in frequency than the second one, and hence w 1 > w 2 , which is reasonable.
  • the Taylor expansion is good if c 1 and c 2 are not too large.
  • the frequency error can be determined from a weighted sum of the measured phase rotations, which in this case are represented by the complex notation in (12).
  • the pilot cells can be chosen so that the frequency error can be determined from the phase rotation measured between the pilot cells without knowing the level of sub-carrier frequency dependent phase rotation.
  • the two pilot cells of each pair, for which a phase rotation is measured are taken from different sub-carriers and different symbols.
  • the pilot cells of one of the pairs are taken from the same symbol. This effectively means that the phase rotation caused by the different sub-carriers can be estimated from a first pair of pilot cells chosen from one symbol and its effect subtracted from the total phase rotation found between another pair of pilot cells chosen from different symbols.
  • the frequency dependent phase rotation might first be estimated by considering pilots in the same OFDM symbol. Once this is estimated, pilots that are located on different sub-carriers and different symbols can be used for determining the frequency error.
  • the process of estimating the frequency error consists of three steps. First, it is estimated how much the phase is changed if pilots at different sub-carriers are used. This is illustrated in Figure 8 , where the phase difference ⁇ 5 between two pilot cells from symbol n +1, i.e. the pilot cell at sub-carrier l +3 and the pilot cell at sub-carrier l -3, is determined. Again, it is assumed that the sub-carriers are sufficiently close to each other for the phase rotation to be considered as a linear function, and thus that from the measured phase rotation, which in Figure 8 corresponds to a distance of six sub-carriers, a phase rotation per sub-carrier or for three sub-carriers can easily be calculated.
  • ⁇ 5 is the phase rotation measured between two pilot cells in the same symbol ( Figure 8 )
  • ⁇ 6 is the phase rotation measured between two pilot cells from different symbols ( Figure 9 )
  • ⁇ x is the phase rotation relating to the frequency error
  • c 1 and c 2 are the distances in frequency between the pilot cells in Figures 8 and 9 , respectively
  • phase rotation relating to the frequency error can be calculated as a weighted sum of the phase rotations measured for two sets of pilot cells.
  • LS Least Squares
  • the frequency error in the FFT gives a linear shift in the phase of the symbols, which depends on the time.
  • the frequency selective channel gives different phase shifts for different, sub-carrier frequencies, which can be any non linear function. If the difference between the maximum and minimum frequencies is not too big and/or the frequency selective channel is approximately linear, it is possible to approximate the phase shift for close frequencies as a linear change, as it has also been assumed for the previous embodiments. Close frequencies could for example be the frequencies in one LTE resource block (i.e. within 180 kHz).
  • n and l are time and sub-carrier for respective pilot and n r is a resource block index.
  • the parameter ⁇ 0 is the base phase for all pilots and all phases are computed relative to this phase.
  • ⁇ f describes the phase shift change due to the frequency selective channel, ⁇ f ⁇ l is the linear approximation of the change.
  • the parameter ⁇ t ( n r )/(2 ⁇ ) is the estimated phase shift due to the frequency error, and hence the parameter of interest.
  • e(n, l ) is introduced in order to take care of non linearity in the frequency selective channel, fading in the channel and noise in the received pilot. It may be described by a sequence of random variables given by some statistical distribution.
  • the phases ⁇ ( n , l ) must be unwrapped in order to not contain any 2 ⁇ jumps.
  • the model contains three unknown parameters (the ⁇ -parameters), which can be estimated by e.g. a least squares approach. If LS estimation of the parameters ⁇ is used then the computations become quite simple.
  • u j 1 n j l j
  • U u 1 ⁇ u N p
  • ⁇ ⁇ n 1 ⁇ l 1 ⁇ ⁇ n N p ⁇ l N p
  • index j is the pilot number
  • u j contains the constant, the time and sub-carrier index for j :th pilot.
  • U describes the locations of the available pilots.
  • Z ( U H U ) -1 U H , then Z is a fixed matrix depending on the locations of the available pilot cells and corresponding to the weighting factors of the previous examples. This fixed matrix can be pre-computed. Since we are only interested in ⁇ t -parameter, the LS calculation becomes N p multiplications and additions.
  • Figure 10 shows a block diagram of a receiver 1 in which the embodiments described above can be implemented. Signals are received through the antenna 2 and processed by the RF circuit 3. This part of the circuit is well known and will not be described in further detail here. Regarding the pilot cells, the output of the circuit 3 will provide the received pilot cells X n,l , while the corresponding sent pilot cells p n,l are provided by a control circuit 4 connected to a memory 5, since the information content of a pilot cell is known by the receiver and thus stored in the memory 5. The control circuit 4 also selects the pilot cells to be used for the calculations.
  • phase difference ⁇ ( n,l ) For a given pilot cell at position ( n,l ), X n,l and p n,l are compared in the phase detector 6, so that the phase difference ⁇ ( n,l ) between X n,l and p n,l for that pilot cell is provided.
  • the calculating unit 7 calculates the change in phase difference ⁇ x due to the frequency error according to one of the embodiments that have been described above.
  • the error detector 8 the calculated change in phase difference ⁇ x is used to calculate the frequency error, as it has also been described above.
  • step 101 the pilot cells to be used for the estimation are selected, and their positions, i.e. the symbols and the sub-carrier frequencies on which they are transmitted, are determined in step 102.
  • step 103 the received pilot cells X n,l and the corresponding sent pilot cells p n,l are compared to determine the phase difference ⁇ n,l for each selected pilot cell.
  • step 104 the change in phase difference ⁇ x due to the frequency error is calculated according to one of the embodiments that have been described above. This step will be described in further detail below for some of the embodiments.
  • step 105 the calculated change in phase difference ⁇ x is used to calculate the frequency error, as it has also been described above.
  • step 201 a weighting factor is determined for each pair of pilot cells, e.g. p 0 and p 1 respectively p 0 and p 2 in Figure 7 , from the distances in time and sub-carrier frequency between the two pilot cells of the pair.
  • step 202 the change in phase difference ⁇ 1 between the first pair of pilot cells p 0 and p 1 is measured.
  • step 203 the change in phase difference ⁇ 2 between the second pair of pilot cells p 0 and p 2 is measured, and in step 204 the change in phase difference ⁇ x due to the frequency error is calculated as a weighted sum of ⁇ 1 and ⁇ 2 as it was described above in relation to Figure 7 .
  • the flow chart in Figure 13 shows the detailed steps of the calculating step 104 for the embodiment illustrated in Figures 8 and 9 .
  • step 301 the change in phase difference ⁇ 5 between the two pilot cells in the same symbol is measured, so that a sub-carrier dependent change in phase difference can be determined therefrom in step 302.
  • step 303 the change in phase difference ⁇ 6 between the two pilot cells in different symbols is measured, and finally, in step 304 the relevant fraction of ⁇ 5 is subtracted from ⁇ 6 to determine the change in phase difference ⁇ x due to the frequency error as it was described above in relation to Figures 8 and 9 .

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EP07388030.4A 2007-05-03 2007-05-03 Détermination d'une erreur de fréquence dans un récepteur d'un système de communication mdfo sans fil Not-in-force EP1988676B1 (fr)

Priority Applications (4)

Application Number Priority Date Filing Date Title
EP07388030.4A EP1988676B1 (fr) 2007-05-03 2007-05-03 Détermination d'une erreur de fréquence dans un récepteur d'un système de communication mdfo sans fil
PCT/EP2008/055454 WO2008135541A1 (fr) 2007-05-03 2008-05-05 Détermination d'une erreur de fréquence dans un récepteur d'un système de communication sans fil
US12/598,613 US8270509B2 (en) 2007-05-03 2008-05-05 Determining a frequency error in a receiver of a wireless communications system
JP2010504752A JP5309132B2 (ja) 2007-05-03 2008-05-05 無線通信システムの受信機における周波数誤差判定

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EP07388030.4A EP1988676B1 (fr) 2007-05-03 2007-05-03 Détermination d'une erreur de fréquence dans un récepteur d'un système de communication mdfo sans fil

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JP6916840B2 (ja) * 2019-06-26 2021-08-11 株式会社タムラ製作所 情報通信システム及び情報通信装置
CN111628949B (zh) * 2020-05-22 2023-06-02 锐迪科微电子（上海）有限公司 频偏估计方法及装置、存储介质、计算机设备

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CN110121657B (zh) * 2016-09-30 2024-04-09 弗劳恩霍夫应用研究促进协会 基于报文拆分的定位

Also Published As

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JP5309132B2 (ja) 2013-10-09
EP1988676B1 (fr) 2019-02-20
JP2010526457A (ja) 2010-07-29
US20100135423A1 (en) 2010-06-03
WO2008135541A1 (fr) 2008-11-13
US8270509B2 (en) 2012-09-18

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